This invention relates to apparatus for automatic placement of flat objects, e.g., placing semiconductor wafers in carriers or boats.
It is desirable to rapidly and automatically transfer semiconductor wafers from plastic storage boats to quartz processing boats (in which they are introduced into a diffusion furnace), and vice versa, without introducing contamination onto the surfaces of the wafers. Such contamination often results during wafer placement in the quartz boats, from the wafers scraping against the slots into which they are placed. Contamination can also arise from scraping and sliding of parts within the apparatus being used to accomplish the transfer.
U.S. Pat. No. 4,493,606 which is hereby incorporated by reference, disclose prior wafer transfer handling apparatus having two trolleys (one for a quartz boat and one for plastic boats) movable along parallel directions, and a vacuum pickup arm that moves in a transverse direction and engages different wafers in different slots in the boats as the trolleys move the slots into position. In using the apparatus described in this patent, the fronts and backs of the wafers are typically in the same orientation in the plastic and quartz boats. If it is desired to change the orientation of the faces of semiconductor wafers between their removal from plastic storage boats and their deposit in quartz boats, for example to place wafers back-to-back to affect wafer treatment, the wafers have to be transferred either by hand or by rotating a carrier, e.g., in a mass transfer system, something that can result in contamination of and damage to the wafers.